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HMAC-based One Time Password generator with code delivery via NDEF format on JavaCard

JavaCard HMAC-based One Time Password generator which delivers new code via URL tag of NDEF every time the card is put close to NFC-enabled phone.

As a result, phone will display prompt to visit URL with current OTP code. No installation of phone software is required. The server side needs to parse OTP code properly from URL request.

Initialization

To avoid initialization problems:

• first upload the HOTP secret. Example: otpauth://hotp/?secret=GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ=&digits=6
• then upload the desired URL. Example: http://hotp.zelitomas.cf/?key=

Both tags must be uploaded separately (i.e. not simultaneously as possible with NFC Tools.

More detailed instructions with screenshots are available on the project wiki.

Setting URL

Using nfc tag writing application (like NFC Tools) write URL to which you would like to be redirected , for example

http://hotp.zelitomas.cf/?key=

Code will be appended to the URL, like this:

http://hotp.zelitomas.cf/?key=1825523596

Check the address by tapping your card to NFC-enabled phone (simple counter is used to generate codes until you set the secret)

Setting HOTP secret

The card accepts otpauth URLs in this format:

otpauth://hotp/username@server/?secret=[base32 encoded secret]

(Google Authenticator HOTP URL without counter parameter)

Write with your favorite NFC tag writing application. Counter is always set to 0 when new secret is set. Also, we recommend setting the required number of digits:

otpauth://hotp/username@server/?secret=[base32 encoded secret]&digits=[desired number of digits]

Credits

The project is based on:

1. NDEF applet by I. Albrech (NDEF applet)